In order to aim a surveying instruments' telescope onto a predetermined target point it is known to use an overview image from a camera on a display. To verify the correct aiming at the target point, it is known to magnify a sector of the overview image. These two images can be alternatingly displayed according to an action of a user.
For example, document EP 1 610 092 A1 discloses a surveying instrument comprising first and second image pickup units. The second image picked up has a higher magnification than the first image picked up. When the first image is displayed on a display, its magnification can be digitally changed in a predetermined range. At an upper limit of the predetermined range effected by switching a zoom changeover switch, the second image is displayed. The magnification of the second image can be also digitally changed.